The present invention relates to constant fluid flow regulators and more particularly to a flow regulator having a spring biased piston and being capable of maintaining a constant fluid flow rate in both high pressure, low volume and low pressure, high volume environments with changes in inlet or outlet pressure. The present invention also accommodates high pressure, high volume and low pressure, low volume systems. Most prior art constant fluid flow regulators vary fluid flow through the piston by movement of the piston that varies the flow pressure through this piston or by change in the spring tension. More specifically, constant fluid flow regulators taught in the prior art regulate fluid flow by adjustment screws that directly vary spring tension by attachment to the piston spring itself. Other regulators change fluid flow by altering piston position via springs and ball bearings located over the piston. The system employing springs and ball bearings is subject to extreme torque due to the fluid pressure in the chamber.
Additionally, multiple poppet type valves may be used for low pressure, high volume fluid flow regulation. The above prior art, however generally cannot accommodate high pressure, low volume fluid flow. This invention, on the other hand, is able to provide constant fluid flow in high or low pressure and high or low volume ranges. The present invention is also different from the above sliding sleeve and multiple poppet type valves in that the piston of the valves of the prior art move relative to the valve body to vary fluid flow as the pressure changes, while the piston of the present invention does not move substantially relative to the valve body after fluid flow has stabilized. Instead, constant spring force on the piston in the present invention allows constant pressure across the piston, therefore the flow is constant. The present invention thus experiences less wear and tear from moving parts.
Furthermore, U.S. Pat. No. 4,893,649 issued to Skoglund and U.S. Pat. No. 3,958,596 issued to Gerrard both disclose valves in which fluid flow variation is implemented by an adjustable valve seat. Adjustment of the valve seat adjusts the spring tension, which in turn alters the pressure differential across the piston. However, both of the above prior art patents employ threaded, screw-type mechanisms for adjusting the valve seat which are difficult to operate, have a narrow operating range, and are prone to breakage in high pressure environments.
Also, the screw-type valve seat adjustment mechanisms of the above prior art references both impede fluid flow through the valve. U.S. Pat. No. 4,893,649, discloses a valve in which the fluid outlet is oriented perpendicular to the fluid inlet in order to accommodate the valve seat adjustment mechanism. This angled fluid flow pathway results in a more complex valve design as well as increased fluid turbulence and higher pressure drops. U.S. Pat. No. 3,958,596 issued to Gerrard teaches a valve in which the fluid outlet passes axially through the valve seat adjustment screw. This valve seat adjustment mechanism configuration is difficult to use while the valve is in operation.
The constant flow rate controller valves discussed in U.S. Pat. Nos. 5,143,116 and 5,234,025, both issued to Skoglund, operate based on the following force balance equations. EQU P.sub.1 A.sub.piston =P.sub.2 (A.sub.piston -A.sub.pin)+KX+P.sub.3 A.sub.pin
Where
P.sub.1 =pressure in the first chamber PA1 A.sub.piston =surface area of the piston PA1 P.sub.2 =pressure in the second chamber PA1 KX=spring force of the springs PA1 A.sub.pin =surface area of the piston pin which mates with the seat PA1 P.sub.3 =pressure at the outlet port PA1 Q=flow rate PA1 P.sub.1 =pressure in the first chamber PA1 P.sub.2 =pressure in the second chamber PA1 C.sub.v =flow resistance across the orifice PA1 Sg=Specific gravity of fluid PA1 P.sub.3 =pressure at the outlet port PA1 A.sub.pin =surface area of the piston pin
Rearrangement of terms produces the following equations: ##EQU1##
Because A.sub.pin is small in comparison to A.sub.piston, and assuming P.sub.3 equals the flow pressure at the outlet port, the following equations characterize the force balance existing in these inventions. EQU KX=(P.sub.1 -P.sub.2)A.sub.piston +P.sub.2 A.sub.pin -P.sub.3 A.sub.pin (P.sub.2 A.sub.pin and P.sub.3 A.sub.pin being relatively small in size) EQU KX.apprxeq.(P.sub.1 -P.sub.2)A.sub.piston
Thus, the differential pressure (P.sub.1 -P.sub.2) is a function of spring force (KX), but is not precisely equal to spring force (KX).
The flow rate of water, for example, through a control valve is defined by the following equation: ##EQU2## Where .DELTA.P=P.sub.1 -P.sub.2
Note that because differential pressures (P.sub.1 -P.sub.2) is a function of spring force (KX), flow rate (Q) is also a function of spring force. Thus, these constant flow rate controller valves have a constant flow as long as spring force remains constant. This flow is constant regardless of the flow pressure at the inlet port. However, there is a pressure force exerted on the piston pin which mates with the valve seat, and against the remainder of piston defined by EQU P.sub.3 .multidot.A.sub.pin
Where
The above force must be minimized for these valves to function pressure independently. Therefore, for the valves to function, the surface area of the piston pin must be small when compared to the surface area of the piston as a whole. Note that this force would not be small and the flow rate would not be constant if the area of the piston pin was not small in value when compared to the surface area of the piston as a whole. These valves therefore can have a limited number of different configurations, and must usually be relatively large.
However, in this invention the following equations apply: EQU P.sub.1 A.sub.1 =P.sub.2 A.sub.2 +KX EQU A.sub.1 =A.sub.2 EQU P.sub.1 A.sub.1 -P.sub.2 A.sub.1 =KX EQU (P.sub.1 -P.sub.2)A.sub.1 =KX ##EQU3##
The area of the outlet A.sub.3 and outlet pressure P.sub.3 are no longer factors in the balance equation on the underside of the piston. These forces are transferred to the body and not to the piston. Therefore the P.sub.1 -P.sub.2 valve across the piston and control surfaces is not impacted by P.sub.3 and A.sub.3. This is a change from the prior art.